Method and system for aiding landing of an aircraft

ABSTRACT

A method for aiding the landing of an aircraft on a landing runway comprises the following steps implemented in an automatic manner by a processing unit: a) acquiring information relating to the landing runway; b) acquiring information relating to a current situation of the aircraft; c) determining, as a function of said information, at least one deviation between at least one parameter relating to a landing position of the aircraft on the landing runway and a reference relating to a central longitudinal axis of the landing runway; d) comparing this deviation with a predetermined threshold; and e) as a function of the result of the comparison carried out in step d), commanding, if appropriate, the signaling of an alert by means of a signaling system of the aircraft.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the French patent application No.1561787 filed on Dec. 3, 2015, the entire disclosures of which areincorporated herein by way of reference.

BACKGROUND OF THE INVENTION

The invention relates to a method and to a system for aiding landing ofan aircraft on a landing runway, as well as to an aircraft comprisingsuch a system.

During an approach phase before a landing, an aircraft is generallyobliged to follow an approach axis of a landing runway, up to a landingposition of the aircraft on the landing runway, for which the wheels ofthe aircraft touch the landing runway (so-called “touchdown” position).This approach axis can, for example, correspond to an axis of aninstrument-based approach of ILS (“Instrument Landing System”) typeImmediately after landing, the aircraft performs a rollout on thelanding runway according to a substantially rectilinear trajectory closeto a central longitudinal axis of the landing runway.

FIG. 1 illustrates, viewed from above, an exemplary approach to alanding runway 5 by an aircraft 1. FIG. 2 corresponds to a more detailedview around the landing position of the aircraft on the landing runway.This approach is also illustrated, in a side view, by FIG. 3. In manualpiloting mode, during the approach phase, the pilot must pilot theaircraft 1 along the closest possible trajectory 12 to the approach axis10 in such a way that, on the one hand, the landing position Td of theaircraft on the landing runway is as close as possible to the centrallongitudinal axis 4 of the landing runway (so as to avoid putting theaircraft down alongside the landing runway) and that, on the other hand,the speed vector Vtd of the aircraft at this landing position issubstantially parallel to the central longitudinal axis of the landingrunway (so as to avoid exiting the runway, laterally, during rolloutafter landing). If a risk of exiting the runway laterally exists, thepilot must perform a go-around and carry out a new approach. During theapproach to the landing runway, in particular during the final phase ofthe approach, the pilot must therefore monitor the trajectory of theaircraft so as to be able to detect such a risk. Document FR2948468 A1describes a method and a device for aiding the lateral control of anaircraft during the approach phase, making it possible to signal acaution in the cockpit of the aircraft in case a risk of lateral exitfrom the landing runway is predicted. It would however be beneficial tohave alternatives to this method and to this device.

SUMMARY OF THE INVENTION

The present invention relates to a method for aiding the landing of anaircraft on a landing runway, the aircraft comprising a set ofinformation sources, a flight management system, a processing unit and asignaling system. The method is noteworthy in that it comprises thefollowing steps implemented in an automatic manner by the processingunit:

-   -   a) acquiring, from the flight management system, information        relating to the landing runway;    -   b) acquiring, from the set of information sources, information        relating to a current situation of the aircraft;    -   c) determining, as a function, on the one hand, of the        information relating to the current situation of the aircraft        and, on the other hand, of the information relating to the        landing runway, at least one deviation between, on the one hand,        at least one parameter relating to a landing position of the        aircraft on the landing runway and, on the other hand, a        reference relating to a central longitudinal axis of the landing        runway;    -   d) comparing this deviation with a predetermined threshold; and    -   e) as a function of the result of the comparison carried out in        step d), commanding, if appropriate, the signaling of an alert        by means of the signaling system of the aircraft.

Thus, by virtue of the signaling of an alert in the cockpit of theaircraft, this method makes it possible to forewarn a crew member, inparticular a pilot of the aircraft, of a risk of lateral exit from therunway. It thus makes it possible to improve safety since the pilot canthen act accordingly to avoid this risk of runway exit, by correctingthe trajectory of the aircraft if this is possible without additionalrisk or by carrying out a go-around so as to attempt a new approach.

In a first variant:

-   -   in step c), the at least one parameter corresponds to the        landing position of the aircraft on the landing runway and the        at least one deviation corresponds to a deviation between, on        the one hand, the landing position of the aircraft on the        landing runway and, on the other hand, the central longitudinal        axis of the landing runway;    -   in step d), this deviation is compared with a predetermined        distance threshold; and    -   in step e), the processing unit commands the signaling of the        alert if this deviation is greater, in absolute value, than this        predetermined distance threshold.

In a second variant:

-   -   in step b), the information relating to the current situation of        the aircraft comprises a current roll angle of the aircraft;    -   in step c), the at least one parameter corresponds to the        landing position of the aircraft on the landing runway and the        at least one deviation corresponds to a deviation between, on        the one hand, the landing position of the aircraft on the        landing runway and, on the other hand, the central longitudinal        axis of the landing runway;    -   in step d), this deviation is compared with a predetermined        distance threshold and the current roll angle is compared with a        predetermined roll angle threshold; and    -   in step e), the processing unit commands the signaling of the        alert if the following conditions all hold:        -   the deviation is greater, in absolute value, than this            predetermined distance threshold;        -   the current roll angle is greater, in absolute value, than            the predetermined roll angle threshold; and        -   the current roll angle tends to deviate the landing position            of the aircraft on the landing runway from the central            longitudinal axis of the landing runway.

In a third variant:

-   -   in step c), the at least one parameter corresponds to a speed        vector of the aircraft at its landing position on the landing        runway and the at least one deviation corresponds to an angular        deviation between, on the one hand, this speed vector and, on        the other hand, a direction of the central longitudinal axis of        the landing runway;    -   in step d), this deviation is compared with a predetermined        angular threshold; and    -   in step e), the processing unit commands the signaling of the        alert if this deviation is greater, in absolute value, than this        predetermined angular threshold.

In a particular embodiment, steps a), b), c), d) and e) are implementedin an automatic and repetitive manner as long as a current height of theaircraft is greater than a predetermined height threshold, the methodfurthermore comprising the following steps implemented in an automaticmanner by the processing unit when the current height of the aircraft isless than this predetermined height threshold:

-   -   a) acquiring, from the flight management system, information        relating to the landing runway;    -   b) acquiring, from the set of information sources, information        relating to a current situation of the aircraft;    -   f) determining a maximum roll angle, in absolute value,        necessary to allow a flight of the aircraft along a trajectory        between a current position of the aircraft and a target landing        position of the aircraft on the landing runway;    -   g) comparing this maximum roll angle with a predetermined roll        angle limit; and    -   h) as a function of the result of the comparison carried out in        step g), commanding, if appropriate, the signaling of an alert        by means of the signaling system of the aircraft.

In another particular embodiment, steps a), b), c), d) and e) areimplemented in an automatic and repetitive manner as long as a currentheight of the aircraft is greater than a predetermined height threshold,the method furthermore comprising the following steps implemented in anautomatic manner by the processing unit when the current height of theaircraft is less than this predetermined height threshold:

-   -   a) acquiring, from the flight management system, information        relating to the landing runway;    -   b) acquiring, from the set of information sources, information        relating to a current situation of the aircraft;    -   i) determining, as a function, on the one hand, of the        information relating to the current situation of the aircraft        and, on the other hand, of the information relating to the        landing runway, a landing position of the aircraft on a central        longitudinal axis of the landing runway, this landing position        being determined as a function of a trajectory determined        between a current position of the aircraft and this landing        position so as to comply with at least one constraint relating        to a roll angle of the aircraft;    -   j) determining a parameter relating to the landing position of        the aircraft on the central longitudinal axis of the landing        runway;    -   k) determining a deviation between this parameter and a        reference value;    -   l) comparing this deviation with a predetermined threshold; and    -   m) as a function of the result of the comparison carried out in        step l), commanding, if appropriate, the signaling of an alert        by means of the signaling system of the aircraft.

The invention also relates to a system for aiding landing of an aircrafton a landing runway, the aircraft comprising a set of informationsources, a flight management system and a signaling system. The systemfor aiding landing is noteworthy in that it comprises a processing unitconfigured to implement the following steps:

-   -   a) acquiring, from the flight management system, information        relating to the landing runway;    -   b) acquiring, from the set of information sources, information        relating to a current situation of the aircraft;    -   c) determining, as a function, on the one hand, of the        information relating to the current situation of the aircraft        and, on the other hand, of the information relating to the        landing runway, at least one deviation between, on the one hand,        at least one parameter relating to a landing position of the        aircraft on the landing runway and, on the other hand, a        reference relating to a central longitudinal axis of the landing        runway;    -   d) comparing this deviation with a predetermined threshold; and    -   e) as a function of the result of the comparison carried out in        step d), commanding, if appropriate, the signaling of an alert        by means of the signaling system of the aircraft.

In a first variant, the processing unit is configured in such a waythat:

-   -   in step c), the at least one parameter corresponds to the        landing position of the aircraft on the landing runway and the        at least one deviation corresponds to a deviation between, on        the one hand, the landing position of the aircraft on the        landing runway and, on the other hand, the central longitudinal        axis of the landing runway;    -   in step d), this deviation is compared with a predetermined        distance threshold; and    -   in step e), the processing unit commands the signaling of the        alert if this deviation is greater, in absolute value, than this        predetermined distance threshold.

In a second variant, the processing unit is configured in such a waythat:

-   -   in step b), the information relating to the current situation of        the aircraft comprises a current roll angle of the aircraft;    -   in step c), the at least one parameter corresponds to the        landing position of the aircraft on the landing runway and the        at least one deviation corresponds to a deviation between, on        the one hand, the landing position of the aircraft on the        landing runway and, on the other hand, the central longitudinal        axis of the landing runway;    -   in step d), this deviation is compared with a predetermined        distance threshold and the current roll angle is compared with a        predetermined roll angle threshold; and    -   in step e), the processing unit commands the signaling of the        alert if the following conditions all hold:        -   the deviation is greater, in absolute value, than this            predetermined distance threshold;        -   the current roll angle is greater, in absolute value, than            the predetermined roll angle threshold; and        -   the current roll angle tends to deviate the landing position            of the aircraft on the landing runway from the central            longitudinal axis of the landing runway.

In a third variant, the processing unit is configured in such a waythat:

-   -   in step c), the at least one parameter corresponds to a speed        vector of the aircraft at its landing position on the landing        runway and the at least one deviation corresponds to an angular        deviation between, on the one hand, this speed vector and, on        the other hand, a direction of the central longitudinal axis of        the landing runway;    -   in step d), this deviation is compared with a predetermined        angular threshold; and    -   in step e), the processing unit commands the signaling of the        alert if this deviation is greater, in absolute value, than this        predetermined angular threshold.

In a particular embodiment, the processing unit is configured so as to:

-   -   implement steps a), b), c), d) and e) in an automatic and        repetitive manner as long as a current height of the aircraft is        greater than a predetermined height threshold; and    -   implement the following steps in an automatic manner when the        current height of the aircraft is less than this predetermined        height threshold:    -   a) acquiring, from the flight management system, information        relating to the landing runway;    -   b) acquiring, from the set of information sources, information        relating to a current situation of the aircraft;    -   f) determining a maximum roll angle, in absolute value,        necessary to allow a flight of the aircraft along a trajectory        between a current position of the aircraft and a target landing        position of the aircraft on the landing runway;    -   g) comparing this maximum roll angle with a predetermined roll        angle limit; and    -   h) as a function of the result of the comparison carried out in        step g), commanding, if appropriate, the signaling of an alert        by means of the signaling system of the aircraft.

In another particular embodiment, the processing unit is configured soas to:

-   -   implement steps a), b), c), d) and e) in an automatic and        repetitive manner as long as a current height of the aircraft is        greater than a predetermined height threshold; and    -   implement the following steps in an automatic manner when the        current height of the aircraft is less than this predetermined        height threshold:    -   a) acquiring, from the flight management system, information        relating to the landing runway;    -   b) acquiring, from the set of information sources, information        relating to a current situation of the aircraft;    -   i) determining, as a function, on the one hand, of the        information relating to the current situation of the aircraft        and, on the other hand, of the information relating to the        landing runway, a landing position of the aircraft on a central        longitudinal axis of the landing runway, this landing position        being determined as a function of a trajectory determined        between a current position of the aircraft and this landing        position so as to comply with at least one constraint relating        to a roll angle of the aircraft;    -   j) determining a parameter relating to the landing position of        the aircraft on the central longitudinal axis of the landing        runway;    -   k) determining a deviation between this parameter and a        reference value;    -   l) comparing this deviation with a predetermined threshold; and    -   m) as a function of the result of the comparison carried out in        step l), commanding, if appropriate, the signaling of an alert        by means of the signaling system of the aircraft.

The invention also relates to an aircraft comprising a system for aidinglanding such as aforementioned.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on reading the description whichfollows and on examining the appended figures.

FIGS. 1 and 2, already described, illustrate viewed from above anexemplary approach to a landing runway by an aircraft.

FIG. 3, already described, corresponds to a side view of the approachrepresented in FIGS. 1 and 2.

FIG. 4 illustrates a system for aiding landing in accordance with anembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The aircraft 1 comprises a system for aiding landing 20 such asrepresented in FIG. 4. The system 20 comprises a processing unit 24(labeled “PROC” in the figure). This processing unit can in particularform part of a computer of flight commands of the aircraft, for examplea guidance computer of FG (“Flight Guidance”) type, a control computerof FCS (“Flight Control System”) type, etc. The processing unit 24 isconnected at input to a set of information sources 22 of the aircraft,comprising, for example, a monitoring unit 22 a, in particular of MMR(“Multi Mode Receiver”) type, and an inertial platform 22 b of IRS(“Inertial Reference System”) type. The processing unit 24 is connectedto the monitoring unit 22 a by a link 21 a and to the inertial platform22 b by a link 21 b. The processing unit 24 is also connected at inputto a flight management system 32 of the aircraft, for example a computerof FMS (“Flight Management System”) type, by a link 31. The processingunit 24 is connected at output, by a link 25, to a signaling system 30of the aircraft, for example a system of CDS (“Control and DisplaySystem”) type comprising a display unit 28 (labeled DU in the figure for“Display Unit”) and/or a sound signaling device in the cockpit, such asa loudspeaker 29.

During operation, in a first embodiment, the processing unit 24acquires, from the flight management system, information relating to thelanding runway. It also acquires, from the set of information sources22, information relating to a current situation of the aircraft. Thisinformation relating to the current situation of the aircraftcorresponds to at least one subset of the following information: theposition, the speed, the acceleration and the orientation (angle ofroll, angle of attitude, angle of sideslip, etc.) of the aircraft. As afunction of the information relating to the current situation of theaircraft and of the information relating to the landing runway, theprocessing unit 24 determines at least one deviation between, on the onehand, at least one parameter relating to a landing position of theaircraft on the landing runway and, on the other hand, a referencerelating to a central longitudinal axis of the landing runway. Theprocessing unit 24 compares this deviation with a predeterminedthreshold and, as a function of the result of the comparison of thisdeviation with this predetermined threshold, it commands, ifappropriate, the signaling of an alert by means of the signaling system30 of the aircraft.

More precisely, in a first variant of the first embodiment, the at leastone parameter corresponds to the landing position Td of the aircraft onthe landing runway and the at least one deviation corresponds to adeviation Dtd between, on the one hand, the landing position Td of theaircraft on the landing runway and, on the other hand, the centrallongitudinal axis 4 of the landing runway 5, as represented in FIG. 2.The processing unit 24 compares this deviation Dtd with a predetermineddistance threshold and it commands the signaling of the alert if thisdeviation is greater, in absolute value, than the predetermined distancethreshold. The predetermined distance threshold can be chosen as afunction of the width of the landing runway and of characteristics ofthe aircraft, in particular its dimensions and the positions of thevarious landing gear. This predetermined distance threshold can, forexample, be chosen in an interval of 7 meters to 15 meters. The value ofthe predetermined distance threshold can be refined experimentally so asto obtain robust detection of the cases justifying an alert, withoutproducing too many false alerts. To command the signaling of the alert,the processing unit 24 dispatches a signal, through the link 25, to thesignaling system 30 which then triggers a display of the alert on thedisplay unit 28 and/or a sound signal in the cockpit by means of theloudspeaker 29. The deviation Dtd can, for example, be computed usingthe following equation:

Dtd=D+V _(y) ·Ttd+0.5·A _(y) ·Ttd ²

in which:

D is a current deviation, in projection in a horizontal plane, between acurrent position of the aircraft and a straight line passing through thecentral longitudinal axis 4 of the landing runway. Several proceduresare possible for determining the deviation D:

-   -   according to a first procedure, the current position of the        aircraft is measured by at least one of the information sources        22, for example by a GPS (“Global Positioning System”) receiver        of the unit MMR 22 a or by the inertial platform 22 b. The        current position can also correspond to a hybridization of the        measurements carried out by the GPS receiver and by the inertial        platform. The position of the central longitudinal axis 4 of the        landing runway forms part of the information relating to the        landing runway acquired from the flight management system 32 by        the processing unit 24. As a function of the current position of        the aircraft and of the position of the central longitudinal        axis 4 of the landing runway, the processing unit 24 computes        the deviation D such as defined above;    -   according to a second procedure, the set of information sources        22 comprises a receiver of ILS (“Instrument Landing System”)        type. Thus, in the case of an instrument-based approach of ILS        type, this receiver receives signals corresponding in particular        to a beam LOC emitted by an emitter situated on the ground. On        the basis of the signals, the receiver of ILS type (or the        processing unit 24) can estimate, in a known manner, the        deviation between the current position of the aircraft and the        approach axis 10. This deviation corresponds to the deviation D;    -   according to a third procedure, the set of information sources        22 comprises a camera embedded aboard the aircraft and        positioned so as to film ahead of the aircraft. This camera        therefore makes it possible to film a zone comprising the        landing runway. A system for analyzing images is coupled to this        camera: it makes it possible to identify the central        longitudinal axis of the landing runway by using known        techniques, for example a Hough transform. A current height Hgnd        of the aircraft relative to a threshold of the landing runway        also being known aboard the aircraft (by virtue of the set of        information sources 22), the processing unit 24 can determine a        deviation between the current position of the aircraft and the        central longitudinal axis of the landing runway, therefore the        deviation D;

These various procedures may optionally be combined to consolidate theestimation of the deviation D;

Vy is a current lateral speed of the aircraft relative to the ground. Itcorresponds to the projection of the current speed of the aircraftrelative to the ground, on a horizontal axis perpendicular to thecentral longitudinal axis 4 of the landing runway;

Ay is a current lateral acceleration of the aircraft relative to theground. According to a first procedure, it can be obtained by projectingthe current acceleration of the aircraft relative to the ground, on thehorizontal axis perpendicular to the central longitudinal axis 4 of thelanding runway. According to a second procedure, it can be estimatedusing, for example, the following equation:

A _(y) =g·tan φ·cos θ

in which:

g is the acceleration due to gravity;

φ is the current roll angle of the aircraft; and

θ is the current pitch angle of the aircraft.

The values of the angles φ and θ are provided, in a usual manner, by theinertial platform 22 b; and

Ttd is a time interval between a current instant and an estimatedinstant of touchdown of the wheels of the aircraft on the landingrunway, at the landing position Td. The time interval Ttd can inparticular be estimated using the following equation:

${Ttd} = {\frac{H_{gnd}}{- {VS}_{gnd}} + T_{flare}}$

in which:

Hgnd is a current height of the aircraft relative to a threshold of thelanding runway, known aboard the aircraft by virtue of the set ofinformation sources 22;

VSgnd is a current vertical speed of the aircraft relative to theground. It is provided by the set of information sources 22, inparticular by a GPS receiver of the unit MMR 22 a or by the inertialplatform 22 b (or else by hybridization of values provided by the GPSreceiver and by the inertial platform). In the equation, this speed isdefined positive upwards.

Tflare is an optional corrective term making it possible to take accountof the additional time taken by the aircraft to carry out a flaremaneuver on landing. When this term is used, its value can be fixed (forexample 5 seconds) or else result from estimations dependent on theaircraft, its current flight conditions (mass, aerodynamicconfiguration, etc.).

In a second variant of the first embodiment, the information relating tothe current situation of the aircraft comprises a current roll angle φof the aircraft. As in the first variant, the at least one parametercorresponds to the landing position Td of the aircraft on the landingrunway and the at least one deviation corresponds to a deviation Dtdbetween, on the one hand, the landing position Td of the aircraft on thelanding runway and, on the other hand, the central longitudinal axis 4of the landing runway 5. The processing unit 24 compares this deviationDtd with a predetermined distance threshold, as in the first variant.Furthermore, the processing unit 24 compares the current roll angle φwith a predetermined roll angle threshold. This predetermined roll anglethreshold can, for example, be chosen in an interval lying between 3degrees and 5 degrees. The value of the predetermined roll anglethreshold can be refined experimentally so as to obtain robust detectionof the cases justifying an alert, without producing too many falsealerts. The processing unit 24 commands the signaling of the alert ifthe following conditions all hold:

-   -   the deviation Dtd is greater, in absolute value, than the        predetermined distance threshold;    -   the current roll angle φ is greater, in absolute value, than the        predetermined roll angle threshold; and    -   the current roll angle tends to deviate the landing position Td        of the aircraft on the landing runway from the central        longitudinal axis 4 of the landing runway.

In an advantageous manner, the third condition hereinabove correspondsto the following logic equation:

((Dtd>0)AND(φ<0))OR((Dtd<0)AND((φ>0))

with:

Dtd>0 when Td is situated to the left of the central longitudinal axisof the landing runway (seen from the aircraft) and Dtd<0 when Td issituated to the right of the axis;

φ>0 when the aircraft banks to the right (that is to say when the rightwing of the aircraft is lower than the left wing) and φ<0 when theaircraft banks to the left;

AND corresponds to the logical AND operator; and

OR corresponds to the logical OR operator.

In a third variant of the first embodiment, the at least one parametercorresponds to a speed vector Vtd of the aircraft at its landingposition Td on the landing runway and the at least one deviationcorresponds to an angular deviation Atd between, on the one hand, thisspeed vector Vtd and, on the other hand, a direction 4 a of the centrallongitudinal axis 4 of the landing runway. As represented in FIG. 2, thedirection 4 a corresponds to a straight line parallel to the axis 4 andpassing through the landing position Td. The processing unit 24 comparesthis angular deviation Atd with a predetermined angular threshold and itcommands the signaling of the alert if this deviation is greater, inabsolute value, than this predetermined angular threshold. The value ofthe predetermined angular threshold can be chosen to be included in aninterval between 5 degrees and 15 degrees, for example equal to about 10degrees. This value can be refined experimentally so as to obtain robustdetection of the cases justifying an alert, without producing too manyfalse alerts. In an advantageous manner, the processing unit 24determines the angular deviation Atd by means of the following equation:

Atd=Track_(td)−ψ_(track)

in which:

ψtrack is the direction (expressed in degrees) of the centrallongitudinal axis of the landing runway relative to North;

Tracktd is the estimated direction, relative to North, of the speedvector Vtd of the aircraft at the landing position Td. This directioncan be estimated by means of the following equation:

${Track}_{td} = \left\lbrack {{Track} + {\frac{{{Ttd}.g.\tan}\; \phi}{V_{gnd}} \cdot \frac{180}{\pi}}} \right\rbrack_{360}$

in which:

Track is the direction, relative to North, of the current ground speedvector of the aircraft;

Ttd is the aforementioned time interval between the current instant andan estimated instant of touchdown of the wheels of the aircraft on thelanding runway, at the landing position Td;

g is the acceleration due to gravity;

φ is the current roll angle of the aircraft;

Vgnd is the current ground speed of the aircraft; and

[ ]₃₆₀ symbolizes the operator modulo 360 degrees.

The third variant of the first embodiment can be combined with one orthe other of the first or second variants. According to a firstalternative, this combination can be carried out by means of a logicalOR of the conditions of activation of the alerts corresponding to thecombined variants, thereby allowing greater sensitivity in the detectionof cases of alert. According to a second alternative, this combinationcan be carried out by means of a logical AND of the conditions ofactivation of the alerts corresponding to the combined variants, therebyallowing greater immunity to false alerts.

In a second embodiment, the processing unit 24 acquires, from the flightmanagement system 32, information relating to the landing runway. Italso acquires, from the set of information sources 22, informationrelating to a current situation of the aircraft. This informationrelating to the current situation of the aircraft corresponds to atleast one subset of the following information: the position, the speed,the acceleration and the orientation (angle of roll, angle of attitude,etc.) of the aircraft. The processing unit 24 determines a maximum rollangle, in absolute value, necessary to allow a flight of the aircraftalong a trajectory between a current position of the aircraft and atarget landing position of the aircraft on the landing runway. Theprocessing unit 24 compares this maximum roll angle with a predeterminedroll angle limit and, as a function of the result of the comparison ofthe maximum roll angle with the predetermined roll angle limit, itcommands, if appropriate, the signaling of an alert by means of thesignaling system 30 of the aircraft.

In an advantageous manner, the target landing position of the aircrafton the landing runway is situated on the central longitudinal axis 4 ofthe landing runway. This makes it possible to avoid a lateral deviationof the landing position of the aircraft on the landing runway, withrespect to the central longitudinal axis.

The processing unit 24 determines a trajectory able to be controlled bya pilot of the aircraft so as to rejoin the target landing position fromthe current position of the aircraft. The maximum roll angle correspondsto the largest roll angle (in absolute value) necessary for a flight ofthe aircraft 1 along the trajectory.

The predetermined roll angle limit is chosen so as to correspond to amaximum roll angle that a pilot of the aircraft can control at thecurrent height of the aircraft relative to the ground, without takingany risk of collision of a part of the aircraft (in particular a wingtip) with the terrain. This limit can correspond to a fixed value orelse depend on other parameters, such as, for example, the height of theaircraft relative to the terrain or to the threshold of the landingrunway, or else the current ground speed of the aircraft. For example,for a height of the aircraft relative to the threshold of the landingrunway of less than 100 feet (about 30 meters), the predetermined rollangle limit can be chosen substantially equal to 3 degrees.

When the result of the comparison of the maximum roll angle with thepredetermined roll angle limit is such that the maximum roll angle isgreater, in absolute value, than the predetermined roll angle limit, theprocessing unit 24 dispatches a signal, through the link 25, to thesignaling system 30 which then triggers a display of the alert on thedisplay unit 28 and/or a sound signal in the cockpit by means of theloudspeaker 29.

In a still advantageous manner, the processing unit 24 computes themaximum roll angle φ Tmax by means of the following equation:

${\phi \; T\; \max} = {{Arctan}\left( \frac{- \left( {D + {V_{y}.T_{td}}} \right)}{{0.5.T_{td}^{2}.g.\cos}\; \theta} \right)}$

in which the parameters D, Vy, Ttd, g and θ are such as defined withreference to the first embodiment.

This value of the maximum roll angle corresponds to a case in which thetrajectory between the current position of the aircraft and the targetlanding position is such that it makes it possible to cancel the lateraldeviation D after a time Ttd with respect to the current instant,therefore when landing at the target landing position. This trajectoryis substantially parabolic between the current position of the aircraftand the target landing position and the roll angle necessary to fly thistrajectory is substantially constant and equal to φTmax along thetrajectory.

In a third embodiment, the processing unit 24 acquires, from the flightmanagement system 32, information relating to the landing runway. Italso acquires, from the set of information sources 22, informationrelating to a current situation of the aircraft. This informationrelating to the current situation of the aircraft corresponds to atleast one subset of the following information: the position, the speed,the acceleration and the orientation (angle of roll, angle of attitude,etc.) of the aircraft. As a function of the information relating to thecurrent situation of the aircraft and of the information relating to thelanding runway, the processing unit 24 determines a landing position ofthe aircraft on the central longitudinal axis 4 of the landing runway,this landing position being determined as a function of a trajectorydetermined between a current position of the aircraft and this landingposition so as to comply with at least one constraint relating to a rollangle of the aircraft. The processing unit 24 thereafter determines aparameter relating to the landing position of the aircraft on thecentral longitudinal axis of the landing runway as well as a deviationbetween this parameter and a reference value. The processing unit 24compares this deviation with a predetermined threshold, and then, as afunction of the result of the comparison carried out between thisdeviation and this predetermined threshold, it commands, if appropriate,the signaling of an alert by means of the signaling system 30 of theaircraft.

In an advantageous manner, the constraint relating to the roll angle ofthe aircraft comprises:

-   -   a first condition according to which the roll angle must be less        than or equal (in absolute value) to a maximum value of roll        angle during a flight of the aircraft along the trajectory;        and/or    -   a second condition according to which the derivative with        respect to time of the roll angle must be less than or equal (in        absolute value) to a maximum value of roll rate during a flight        of the aircraft along the trajectory.

For the first condition, the maximum value of roll angle is chosen so asto correspond to a roll angle that a pilot of the aircraft can controlat the current height of the aircraft relative to the ground, withouttaking any risk of collision of a part of the aircraft (in particular awing tip) with the terrain. This maximum value can correspond to a fixedvalue or else depend on other parameters, such as, for example, theheight of the aircraft relative to the terrain or to the threshold ofthe landing runway, or else the current ground speed of the aircraft.This value can, for example, be chosen substantially equal to 3 degreeswhen the height of the aircraft relative to the threshold of the landingrunway is less than 100 feet (about 30 meters). For the secondcondition, the maximum value of roll rate is chosen so as to correspondto a roll rate that a pilot of the aircraft can control at the currentheight of the aircraft relative to the ground, without taking any riskof collision of a part of the aircraft (in particular a wing tip) withthe terrain and/or without fearing to take such a risk. This maximumvalue can correspond to a fixed value or else depend on otherparameters, such as, for example, the height of the aircraft relative tothe terrain or to the threshold of the landing runway, or else thecurrent ground speed of the aircraft. This value can, for example, bechosen substantially equal to 2 degrees per second when the height ofthe aircraft relative to the threshold of the landing runway is lessthan 100 feet (about 30 meters).

According to one possibility, the parameter relating to the landingposition of the aircraft on the central longitudinal axis of the landingrunway corresponds to a distance between the current position of theaircraft and the landing position, this distance being considered inprojection on a straight line parallel to the central longitudinal axisof the landing runway. In a particular manner, the reference valuecorresponds to a current landing distance determined as a function ofthe information relating to the current situation of the aircraft. Theterm current landing distance designates here a landing distanceestimated at the current instant as a function of the informationrelating to the current situation of the aircraft. This current landingdistance is, for example, determined using the following formula:

D _(ldg) =V _(x) ·T _(td)

in which:

Dldg is the current landing distance;

Vx is the current speed of the aircraft relative to the ground,considered in projection on a straight line parallel to the centrallongitudinal axis of the landing runway;

Ttd is a time interval between a current instant and an instant oflanding of the aircraft. This time interval can be computed as indicatedpreviously with reference to the first embodiment.

The processing unit 24 determines a deviation between, on the one hand,the distance between the current position of the aircraft and thelanding position and, on the other hand, the current landing distanceDldg. The processing unit 24 compares this deviation with apredetermined threshold. If this deviation is greater than thepredetermined threshold, the processing unit 24 commands the signalingof an alert by means of the signaling system 30 of the aircraft. Thevalue of the predetermined threshold can be chosen equal to a distancemargin of a few tens or hundreds of meters, for example about 200meters, in such a way that the processing unit 24 commands the signalingof the alert when the distance between the current position of theaircraft and the landing position is greater than the current landingdistance Dldg plus the distance margin.

To determine the distance between the current position of the aircraftand the landing position, the processing unit 24 firstly determines thetrajectory between the current position of the aircraft and the landingposition. Accordingly, at the current position of the aircraft, thespeed vector of the aircraft along the trajectory is considered to bealigned with the current course of the aircraft. The landing position isconsidered on the central longitudinal axis 4 of the landing runway(without, however, this landing position being frozen longitudinally onthis axis), the speed vector of the aircraft then being aligned with thecentral longitudinal axis. The processing unit 24 determines thetrajectory using a known procedure for trajectory generation, whilecomplying with the constraint relating to the roll angle of theaircraft, corresponding, for example, to a maximum value of roll angleof 3 degrees (in absolute value) and to a maximum roll rate of 2 degreesper second (in absolute value) as mentioned previously. Among the knownprocedures for trajectory generation, it is, for example, possible touse Dubins curves (succession of clothoids, of circular arcs, ofstraight lines, etc.), splines (for example Bezier curves), etc. Theseprocedures can be implemented analytically (by considering apredetermined string of trajectory elements such as circular arcs,straight lines, etc.) or numerically (by searching for curves thatoptimize the curvature and the derivative of the curvature). Once thetrajectory has been determined by the processing unit 24, the landingposition is likewise determined from a longitudinal point of view on thecentral longitudinal axis 4 of the landing runway. The processing unit24 then computes the distance between the current position of theaircraft and the landing position, in projection on a straight lineparallel to the central longitudinal axis 4 of the landing runway.

Alternatively, the distance between the current position of the aircraftand the landing position can be computed by using a table comprising asinputs values of lateral deviation of the aircraft with respect to theapproach axis, values of angular deviation between the current speedvector of the aircraft and the approach axis and values of height of theaircraft, this table providing as output values of distance between thecurrent position of the aircraft and the landing position on the centrallongitudinal axis of the landing runway. This table can, for example, beutilized as is by the processing unit 24 (optionally with the aid ofinterpolation techniques), or else be utilized in the form of a neuralnetwork.

The third embodiment can be combined with the second embodiment.According to a first alternative, this combination can be carried out bymeans of a logical OR of the conditions of activation of the alertscorresponding to these two embodiments, thereby allowing greatersensitivity in the detection of cases of alert. According to a secondalternative, this combination can be carried out by means of a logicalAND of the conditions of activation of the alerts corresponding to thesetwo embodiments, thereby allowing greater immunity to false alerts.

In a first particular embodiment, the first embodiment (whichevervariant is considered) is implemented when the current height of theaircraft relative to a threshold of the landing runway is greater than afirst predetermined height threshold A1, for example 100 feet (about 30meters), as represented in FIG. 3. The alert, the signaling of which isoptionally commanded by the system for aiding landing, then correspondsto an alert of “warning” type making it possible to signal to the pilotof the aircraft that he must correct the current situation of theaircraft in order to avoid exiting the runway laterally. The height ofthe aircraft relative to the terrain is then considered sufficient forthe pilot to be able to attempt a maneuver to correct the trajectory ofthe aircraft so as to avoid exiting the runway laterally, without takingany risk in respect of the safety of the aircraft. Even if he does notsucceed in correcting the trajectory of the aircraft sufficiently, thepilot is thus informed in advance of a risk of exiting the runwaylaterally, thereby allowing him to prepare himself to effect a go-aroundin order to attempt a new approach. In an advantageous, althoughoptional, manner, the first embodiment is implemented only from thepoint in time when the current height of the aircraft relative to thethreshold of the landing runway is less than a second predeterminedheight threshold A2, for example 200 feet (about 60 meters), asrepresented in FIG. 3. This makes it possible for the alert of warningtype to be signaled only when the aircraft is sufficiently close to thelanding runway so as to avoid untimely alerts in the cockpit.

In a second particular embodiment, that can optionally be combined withthe first particular embodiment, the second embodiment and/or the thirdembodiment (optionally combined with one another as indicatedpreviously) are implemented when the current height of the aircraftrelative to the threshold of the landing runway is less than the firstpredetermined height threshold A1, for example 100 feet (about 30meters). The alert, the signaling of which is optionally commanded bythe system for aiding landing, then corresponds to an alert of “caution”type making it possible to signal to the pilot of the aircraft that hecan no longer correct the trajectory of the aircraft in order to avoidexiting the runway laterally, without taking some other risk, and thathe must then carry out a go-around in order to attempt a new approach.Indeed, the height of the aircraft relative to the terrain is then nolonger sufficient to carry out a maneuver to correct the trajectory ofthe aircraft without the risk either of touching the ground with a wingtip if the trajectory correction requires too high a roll angle, or oflanding at a landing position that is too close to the end of the runwayif the trajectory correction is carried out with a lower roll angle, orelse of bringing about a situation in which the pilot would not be ableto control the dynamics of the aircraft to stabilize it while landing atthe landing position.

In another particular embodiment, the first embodiment can also beimplemented when the current height of the aircraft relative to thethreshold of the landing runway is less than the first predeterminedheight threshold A1. In such a case, the different variants can be usedalone or combined with one another as indicated above. The secondvariant exhibits a greater interest than the other two insofar as ittakes account of the current roll angle of the aircraft. These differentvariants can also be combined with the second embodiment and/or with thethird embodiment so as to improve the detection of alerts. When thefirst embodiment is implemented while the current height of the aircraftrelative to the threshold of the landing runway is less than the firstpredetermined height threshold A1, in an advantageous manner theprocessing unit adapts accordingly the predetermined threshold withwhich the deviation between, on the one hand, the parameter relating tothe landing position of the aircraft on the landing runway and, on theother hand, the reference relating to the central longitudinal axis ofthe landing runway is compared. More particularly, the processing unitreduces the value of the predetermined threshold when the current heightof the aircraft relative to the threshold of the landing runway is lessthan the first predetermined height threshold A1, so as to take accountof the proximity of the ground.

While at least one exemplary embodiment of the present invention(s) isdisclosed herein, it should be understood that modifications,substitutions and alternatives may be apparent to one of ordinary skillin the art and can be made without departing from the scope of thisdisclosure. This disclosure is intended to cover any adaptations orvariations of the exemplary embodiment(s). In addition, in thisdisclosure, the terms “comprise” or “comprising” do not exclude otherelements or steps, the terms “a” or “one” do not exclude a pluralnumber, and the term “or” means either or both. Furthermore,characteristics or steps which have been described may also be used incombination with other characteristics or steps and in any order unlessthe disclosure or context suggests otherwise. This disclosure herebyincorporates by reference the complete disclosure of any patent orapplication from which it claims benefit or priority.

1. A method for aiding the landing of an aircraft on a landing runway,the aircraft comprising a set of information sources, a flightmanagement system, a processing unit and a signaling system, the methodcomprising the following steps implemented in an automatic manner by theprocessing unit: a) acquiring, from the flight management system,information relating to the landing runway; b) acquiring, from the setof information sources, information relating to a current situation ofthe aircraft; c) determining, as a function, on the one hand, of theinformation relating to the current situation of the aircraft and, onthe other hand, of the information relating to the landing runway, atleast one deviation between, on the one hand, at least one parameterrelating to a landing position of the aircraft on the landing runwayand, on the other hand, a reference relating to a central longitudinalaxis of the landing runway; d) comparing this deviation with apredetermined threshold; and e) as a function of the result of thecomparison carried out in step d), commanding, if appropriate, thesignaling of an alert by means of the signaling system of the aircraft,wherein: in step b), the information relating to the current situationof the aircraft comprises a current roll angle of the aircraft; in stepc), said at least one parameter corresponds to the landing position ofthe aircraft on the landing runway and said at least one deviationcorresponds to a deviation between, on the one hand, the landingposition of the aircraft on the landing runway and, on the other hand,the central longitudinal axis of the landing runway; in step d), thisdeviation is compared with a predetermined distance threshold and thecurrent roll angle is compared with a predetermined roll anglethreshold; and in step e), the processing unit commands the signaling ofthe alert if the following conditions all hold: said deviation isgreater, in absolute value, than this predetermined distance threshold;the current roll angle is greater, in absolute value, than thepredetermined roll angle threshold; and the current roll angle tends todeviate the landing position of the aircraft on the landing runway fromthe central longitudinal axis of the landing runway.
 2. The method asclaimed in claim 1, wherein: in step c), said at least one parametercorresponds furthermore to a speed vector of the aircraft at its landingposition on the landing runway and said at least one deviationcorresponds to an angular deviation between, on the one hand, this speedvector and, on the other hand, a direction of the central longitudinalaxis of the landing runway; in step d), this deviation is compared witha predetermined angular threshold; and in step e), the processing unitcommands the signaling of the alert if this deviation is greater, inabsolute value, than this predetermined angular threshold.
 3. The methodas claimed in claim 1, wherein steps a), b), c), d) and e) areimplemented in an automatic and repetitive manner as long as a currentheight of the aircraft is greater than a predetermined height threshold,the method furthermore comprising the following steps implemented in anautomatic manner by the processing unit when the current height of theaircraft is less than this predetermined height threshold: a) acquiring,from the flight management system, information relating to the landingrunway; b) acquiring, from the set of information sources, informationrelating to a current situation of the aircraft; f) determining amaximum roll angle, in absolute value, necessary to allow a flight ofthe aircraft along a trajectory between a current position of theaircraft and a target landing position of the aircraft on the landingrunway; g) comparing this maximum roll angle with a predetermined rollangle limit; and h) as a function of the result of the comparisoncarried out in step g), commanding, if appropriate, the signaling of analert by means of the signaling system of the aircraft.
 4. The method asclaimed in claim 1, wherein steps a), b), c), d) and e) are implementedin an automatic and repetitive manner as long as a current height of theaircraft is greater than a predetermined height threshold, the methodfurthermore comprising the following steps implemented in an automaticmanner by the processing unit when the current height of the aircraft isless than this predetermined height threshold: a) acquiring, from theflight management system, information relating to the landing runway; b)acquiring, from the set of information sources, information relating toa current situation of the aircraft; i) determining, as a function, onthe one hand, of the information relating to the current situation ofthe aircraft and, on the other hand, of the information relating to thelanding runway, a landing position of the aircraft on a centrallongitudinal axis of the landing runway, this landing position beingdetermined as a function of a trajectory determined between a currentposition of the aircraft and this landing position so as to comply withat least one constraint relating to a roll angle of the aircraft; j)determining a parameter relating to said landing position of theaircraft on the central longitudinal axis of the landing runway; k)determining a deviation between this parameter and a reference value; l)comparing this deviation with a predetermined threshold; and m) as afunction of the result of the comparison carried out in step l),commanding, if appropriate, the signaling of an alert by means of thesignaling system of the aircraft.
 5. A system for aiding the landing ofan aircraft on a landing runway, the aircraft comprising a set ofinformation sources, a flight management system and a signaling system,the system for aiding landing comprising a processing unit configured toimplement the following steps: a) acquiring, from the flight managementsystem, information relating to the landing runway; b) acquiring, fromthe set of information sources, information relating to a currentsituation of the aircraft; c) determining, as a function, on the onehand, of the information relating to the current situation of theaircraft and, on the other hand, of the information relating to thelanding runway, at least one deviation between, on the one hand, atleast one parameter relating to a landing position of the aircraft onthe landing runway and, on the other hand, a reference relating to acentral longitudinal axis of the landing runway; d) comparing thisdeviation with a predetermined threshold; and e) as a function of theresult of the comparison carried out in step d), commanding, ifappropriate, the signaling of an alert by means of the signaling systemof the aircraft, wherein the processing unit is configured in such a waythat: in step b), the information relating to the current situation ofthe aircraft comprises a current roll angle of the aircraft; in step c),said at least one parameter corresponds to the landing position of theaircraft on the landing runway and said at least one deviationcorresponds to a deviation between, on the one hand, the landingposition of the aircraft on the landing runway and, on the other hand,the central longitudinal axis of the landing runway; in step d), thisdeviation is compared with a predetermined distance threshold and thecurrent roll angle is compared with a predetermined roll anglethreshold; and in step e), the processing unit commands the signaling ofthe alert if the following conditions all hold: said deviation isgreater, in absolute value, than this predetermined distance threshold;the current roll angle is greater, in absolute value, than thepredetermined roll angle threshold; and the current roll angle tends todeviate the landing position of the aircraft on the landing runway fromthe central longitudinal axis of the landing runway.
 6. The system asclaimed in claim 5, wherein the processing unit is configured in such away that: in step c), said at least one parameter correspondsfurthermore to a speed vector of the aircraft at its landing position onthe landing runway and said at least one deviation corresponds to anangular deviation between, on the one hand, this speed vector and, onthe other hand, a direction of the central longitudinal axis of thelanding runway; in step d), this deviation is compared with apredetermined angular threshold; and in step e), the processing unitcommands the signaling of the alert if this deviation is greater, inabsolute value, than this predetermined angular threshold.
 7. The systemas claimed in claim 5, wherein the processing unit is configured so asto: implement steps a), b), c), d) and e) in an automatic and repetitivemanner as long as a current height of the aircraft is greater than apredetermined height threshold; and implement the following steps in anautomatic manner when the current height of the aircraft is less thanthis predetermined height threshold: a) acquiring, from the flightmanagement system, information relating to the landing runway; b)acquiring, from the set of information sources, information relating toa current situation of the aircraft; f) determining a maximum rollangle, in absolute value, necessary to allow a flight of the aircraftalong a trajectory between a current position of the aircraft and atarget landing position of the aircraft on the landing runway; g)comparing this maximum roll angle with a predetermined roll angle limit;and h) as a function of the result of the comparison carried out in stepg), commanding, if appropriate, the signaling of an alert by means ofthe signaling system of the aircraft.
 8. The system as claimed in claim5, wherein the processing unit is configured so as to: implement stepsa), b), c), d) and e) in an automatic and repetitive manner as long as acurrent height of the aircraft is greater than a predetermined heightthreshold; and implement the following steps in an automatic manner whenthe current height of the aircraft is less than this predeterminedheight threshold: a) acquiring, from the flight management system,information relating to the landing runway; b) acquiring, from the setof information sources, information relating to a current situation ofthe aircraft; i) determining, as a function, on the one hand, of theinformation relating to the current situation of the aircraft and, onthe other hand, of the information relating to the landing runway, alanding position of the aircraft on a central longitudinal axis of thelanding runway, this landing position being determined as a function ofa trajectory determined between a current position of the aircraft andthis landing position so as to comply with at least one constraintrelating to a roll angle of the aircraft; j) determining a parameterrelating to said landing position of the aircraft on the centrallongitudinal axis of the landing runway; k) determining a deviationbetween this parameter and a reference value; l) comparing thisdeviation with a predetermined threshold; and m) as a function of theresult of the comparison carried out in step l), commanding, ifappropriate, the signaling of an alert by means of the signaling systemof the aircraft.
 9. An aircraft comprising: a system for aiding thelanding of an aircraft on a landing runway, a set of informationsources, a flight management system, and a signaling system, the systemfor aiding landing comprising a processing unit configured to implementthe following steps: a) acquiring, from the flight management system,information relating to the landing runway; b) acquiring, from the setof information sources, information relating to a current situation ofthe aircraft; c) determining, as a function, on the one hand, of theinformation relating to the current situation of the aircraft and, onthe other hand, of the information relating to the landing runway, atleast one deviation between, on the one hand, at least one parameterrelating to a landing position of the aircraft on the landing runwayand, on the other hand, a reference relating to a central longitudinalaxis of the landing runway; d) comparing this deviation with apredetermined threshold; and e) as a function of the result of thecomparison carried out in step d), commanding, if appropriate, thesignaling of an alert by means of the signaling system of the aircraft,wherein the processing unit is configured in such a way that: in stepb), the information relating to the current situation of the aircraftcomprises a current roll angle of the aircraft; in step c), said atleast one parameter corresponds to the landing position of the aircrafton the landing runway and said at least one deviation corresponds to adeviation between, on the one hand, the landing position of the aircrafton the landing runway and, on the other hand, the central longitudinalaxis of the landing runway; in step d), this deviation is compared witha predetermined distance threshold and the current roll angle iscompared with a predetermined roll angle threshold; and in step e), theprocessing unit commands the signaling of the alert if the followingconditions all hold: said deviation is greater, in absolute value, thanthis predetermined distance threshold; the current roll angle isgreater, in absolute value, than the predetermined roll angle threshold;and the current roll angle tends to deviate the landing position of theaircraft on the landing runway from the central longitudinal axis of thelanding runway.
 10. The aircraft as claimed in claim 9, wherein theprocessing unit is configured in such a way that: in step c), said atleast one parameter corresponds furthermore to a speed vector of theaircraft at its landing position on the landing runway and said at leastone deviation corresponds to an angular deviation between, on the onehand, this speed vector and, on the other hand, a direction of thecentral longitudinal axis of the landing runway; in step d), thisdeviation is compared with a predetermined angular threshold; and instep e), the processing unit commands the signaling of the alert if thisdeviation is greater, in absolute value, than this predetermined angularthreshold.
 11. The system as claimed in claim 9, wherein the processingunit is configured so as to: implement steps a), b), c), d) and e) in anautomatic and repetitive manner as long as a current height of theaircraft is greater than a predetermined height threshold; and implementthe following steps in an automatic manner when the current height ofthe aircraft is less than this predetermined height threshold: a)acquiring, from the flight management system, information relating tothe landing runway; b) acquiring, from the set of information sources,information relating to a current situation of the aircraft; f)determining a maximum roll angle, in absolute value, necessary to allowa flight of the aircraft along a trajectory between a current positionof the aircraft and a target landing position of the aircraft on thelanding runway; g) comparing this maximum roll angle with apredetermined roll angle limit; and h) as a function of the result ofthe comparison carried out in step g), commanding, if appropriate, thesignaling of an alert by means of the signaling system of the aircraft.12. The system as claimed in claim 9, wherein the processing unit isconfigured so as to: implement steps a), b), c), d) and e) in anautomatic and repetitive manner as long as a current height of theaircraft is greater than a predetermined height threshold; and implementthe following steps in an automatic manner when the current height ofthe aircraft is less than this predetermined height threshold: a)acquiring, from the flight management system, information relating tothe landing runway; b) acquiring, from the set of information sources,information relating to a current situation of the aircraft; i)determining, as a function, on the one hand, of the information relatingto the current situation of the aircraft and, on the other hand, of theinformation relating to the landing runway, a landing position of theaircraft on a central longitudinal axis of the landing runway, thislanding position being determined as a function of a trajectorydetermined between a current position of the aircraft and this landingposition so as to comply with at least one constraint relating to a rollangle of the aircraft; j) determining a parameter relating to saidlanding position of the aircraft on the central longitudinal axis of thelanding runway; k) determining a deviation between this parameter and areference value; l) comparing this deviation with a predeterminedthreshold; and m) as a function of the result of the comparison carriedout in step l), commanding, if appropriate, the signaling of an alert bymeans of the signaling system of the aircraft.